This invention relates to an arrangement of screens intended to give rise to a moire pattern, which pattern is used, for example, for the purposes stated, for example, SE-PS, (patent application No. 7611513-8). corresponding to U.S. patent application Ser. No. 841,121, now U.S. Pat. No. 4,166,699. The present invention, more definitely, relates to the design of the opaque screen lines existing at such screens and separated by transparent interspaces.
In said Se-PS (patent application No. 7611513-8) a screen arrangement is described which is intended to indicate a.o. a certain plane. Said screen arrangement consists of two or more frames and of a plurality of mutually parallel opaque screen lines attached in said frames.
When observing an arrangement according to said Swedish patent, a moire pattern appears which contains information of on which side of a certain plane the observer is or if the observer is in said plane.
The moire pattern formed, however, is conditioned entirely on the division of the different screens, i.e. on the size relation between the opaque and transparent lines, respectively. When the division in one or several screens is changed, thus, a different moire pattern arises.
The screen arrangement described above and in the following is to be regarded only as an example regarding the utilization of the present invention.
It was found that the moire pattern in one and the same screen arrangement comprising at least two screens is changed at certain light conditions without a change of the divisions of the screens having taken place. As a result, the screen arrangement can produce a moire pattern, which is unclear, distorted and in certain cases more or less incorrect relative to the pattern intended. In the lastmentioned case, thus, the intended indicating effect of the moire pattern can be wrong. This problem is greatest at screen arrangements for outdoor use, and especially when the screen arrangements are provided with a lighted up background as stated in said patent, in order to render it possible to read the screen arrangement during the dark hours of a day.
The present invention solves the aforesaid problem.